Me too... the name "rock snot" is what made me think that's what I was looking at. I did read that it's not slimy, and that it feels like wet cotton or as suggested above steel wool. Either way, I got really bummed when I saw it.

Nevertheless, I'm not sure about the pic. Didymo is yellow and tends to bloom out this time of year on rocks....but this is also true for a variety of algeas. If it was local around Philly, I'd contact the PFBC and forward these pics via PM to Mike just to be safe. Didymo does exist in some eastern PA waters and may be spreading.

EDIT: I sent the link to Mike to check out. He may want to know the water involved. Jbomb, you might want to follow up by PMing Mike the name of the stream and area you fished.Dave W

It seems every year around this time I start to see algae that raises this same question in my mind.Probably not but its certainly best to make sure before you start fishing surrounding streams. I would just go back and feel it.